In the present investigation, the AQI level was at its highest peak on year starting among all of the four studied sites i.e., 443 in site 1, 298 in site 2, 292 in site 3, and 166 in site 4. Initial data indicates Delhi was in the hazardous range while poor air quality in other states. Although irregular declining pattern was observed in the AQI level for all of the studied locations, a significant reduction within the pollutant level can be seen after comparing initial and final values. A remarkable drop falls of 44%, 59%, 59%, and 6% in mean concentration of AQI which was observed during COVID-19 pandemic confinement for sites 1, 2, 3, and 4 respectively as shown in Fig. 3.
Fig. 3 Comparative AQI levels during pre-lockdown and lockdown period at 17:00 IST among four different air quality monitoring stations of the CPCB for four major metropolitan cities in India (site 1—ITO, Delhi, site 2—Worli, Mumbai, site 3—Jadavpur, Kolkata, and site 4—Manali Village, Chennai)